1. Field of the Invention
The present general inventive concept relates to an illuminating unit to produce and emit a beam and a projection-type image display apparatus employing the same, and more particularly, to an illuminating unit with a compact design which is capable of improving collimating characteristics of beams emitted by a plurality of light sources at different locations within the illuminating unit, and a projection-type image display apparatus employing the same.
2. Description of the Related Art
In general, an illuminating unit including a non-point light source, such as light-emitting diodes (LEDs), and a reflector with a single curvature is used in an illuminating system for emitting uniform white light and collects a beam emitted by the non-point light source and directs the collected beam in one direction. The illuminating unit typically needs to project a collimated beam by focusing the beam emitted by the non-point light source. However, it is difficult to make the collimated beam using the illuminating unit.
Referring to FIG. 1, a conventional illuminating unit includes an LED package 1 that emits white light, a reflector 3 that reflects a beam emitted by the LED package 1, an entrance aperture 5, and an exit aperture 7. The LED package 1 is constructed to align red, green, and blue LED chips on one plane 3a of the reflector 3 to produce white light by combining beams emitted from the respective LED chips. The plane 3a is parallel to the entrance aperture 5 and the exit aperture 7.
Since the reflector 3 has a polygonal (approximately paraboloidal) cross-section, the beams reflected by the reflector 3 are allowed to exit the reflector 3 through the exit aperture 7 while maintaining good collimating characteristics and color uniformity.
The conventional illuminating unit including the reflector 3 having the polygonal cross-section is advantageous, since the polygonal cross section has improved collimating properties over other illuminating units including mirrors having a parabolic, spherical, or elliptical cross-section.
However, since the conventional illuminating unit having a polygonal reflector has a limitation on reducing its size, a beam spot produced by the conventional illuminating unit has a diameter that is not suitable for use in a projection-type image display apparatus. Thus, the conventional illuminating unit requires a separate focusing system when it is used in a projection-type image display apparatus. Another drawback exists in that it is difficult to realize a compact illuminating unit, since there is a limitation in reducing the size of a reflector.